Conventionally, research has been widely conducted related to techniques for sealing between members to prevent, for example, oil leakage. For example, a method of sealing using an O-ring made of rubber as shown in FIG. 7 is widely known from the viewpoints of simplicity of the structure and the like. In this method, sealing is achieved by utilizing a repelling force (contact pressure) of the O-ring, the repelling force being generated by applying pressure as appropriate to the O-ring that is mounted at a groove portion provided on the member.
However, in a case in which sealing between members is carried out using an O-ring and one of the members is a rotary shaft, the rotational resistance of the rotary shaft is increased and moreover, abrasion of the O-ring occurs easily. Therefore, there is a problem in that the sealing durability is low. This is because sealing between members is carried out by applying contact pressure between the O-ring and the rotary shaft.
Other than the sealing method using an O-ring, an oil seal is known in which a lip portion made of rubber, a metal reinforcing ring, and a spring are provided and the lip tip is pressed against a member such as a rotary shaft by the spring, thereby carrying out sealing. Since grease or the like is loaded in the oil seal, there is concern that the oil component may leak out to pollute the surroundings. Further, since sealing is carried out by utilizing the contact pressure between the lip portion made of rubber and the rotary shaft, dust is generated due to abrasion and there is a problem in that the sealing durability is low.
Further, a technique for sealing is also known in which a magnetic fluid is positioned at a gap between a rotary shaft typified by a shaft and a pole piece, such that the magnetic fluid is held by the magnetic force and the magnetic fluid thus held does not flow out, even if there is a pressure difference. Specifically, a magnetic fluid seal has been disclosed in which, in a sealing structure that seals the annular gap between a shaft member and a housing that is provided concentrically with the shaft member, between the shaft and a pole piece that is a magnetic pole member arranged in the annular gap, the gap between the internal circumferential surface of the pole piece and the outer circumferential surface of the shaft is sealed by a magnetic fluid (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-269623).
Moreover, a technique for sealing using a magnetic powder that is held by a magnetic force is also known. Specifically, a magnetic powder sealing method has been disclosed in which a magnetic brush of a magnetic powder is formed along the magnetic force line using magnetic particles, and, by the magnetic brush thus formed, leakage of the magnetic powder to the outside of the container is prevented (see, for example, JP-A No. H10-26884).